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Jun 1979

Volume 65, Issue S1, pp. S2-S142

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back to top Session LL. Shock and Vibration II: Application of Statistical Energy Analysis
Invited Papers
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The use of SEA in building acoustics (A)

R. Craik and R. K. Mackenzie

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S96-S97 (1979); (2 pages)

Online Publication Date: 11 Aug 2005

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During 1974 a survey was carried out by the International Council of Building to establish the state of knowledge relating to noise and vibration within the built environment. The results of the survey clearly demonstrate the need for a better understanding of the transmission of sound through connected structures, and it was recommended that the solution to these problems would be best achieved by investigating the coupling loss factors between structural elements using SEA methods. During 1975 a meeting of representatives from 19 laboratories from throughout the world was held at Grenoble, France. The outcome of this meeting was the establishment of a program of collaborative studies based on agreed set of research priorities with each laboratory tackling the same problem, but using a different approach. Significant progress has been made to date, particularly in the study of a full scale building in Edinburgh. This study has resulted in the analysis of a large SEA model with 104 subsystems and has given over 150 measured coupling loss factors. These coupling loss factors, which give reasonable agreement with predicted results, are being used to determine the noise reduction of specific acoustic paths.
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Using SEA to model vibration transmission in engine structure (A)

R. G. DeJong

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S97-S97 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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Understanding the vibration characteristics of engine structures is an important aspect of the overall effort to reduce engine noise. Recent advances have been made in the measurement and modeling of the vibration characteristics of the individual components in an engine structure for the purpose of developing an analytical model which predicts the vibration transmission of the complete structure. For components with a small number of resonant modes of vibration in the frequency range of interest, lumped parameter models can be developed which match the vibration response function quite accurately. However, for components with a large number of resonant modes in the frequency range of interest, it is more useful to employ Statistical Energy Analysis to model the average vibration response. This paper demonstrates the comparability of these two types of models and shows some examples of the use of a complete vibration model in identifying component design changes which will result in engine noise reductions. [Work supported by EPA/ONAC.]
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The use of SEA in shipbuilding (A)

Richard H. Lyon

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S97-S97 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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The prediction of vibration and sound transmission in ship structures is a recent and potentially important area of SEA applications. The developments of these applications in the U.S., Europe, and the Far East is reviewed. These developments include both experimental studies and analytical analyses (including computer studies). There are several issues to be resolved in this work which include the role of in‐plane vibration of the hull and the degree to which reverberation in the structure does or does not dominate traveling wave effects.
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Statistical energy analysis prediction of the response of offshore structures to random wave excitation (A)

J. Kim Vandiver

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S97-S97 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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The principle of reciprocity is applied to dynamic response prediction of structures excited by ocean waves. It is shown that the modal wave force spectrum may be expressed in terms of the modal radiation damping coefficient. This leads to the familiar SEA result: that the damping controlled response of the resonator (a mode of an offshore structure) has an upper bound, which occurs when the ratio of the radiation to the total damping approaches unity. This result is embodied in a general method for predicting the damping controlled response of a broad variety of ocean structures. The method includes the effects of the highly directional nature of ocean wave spectra. Example calculations are presented for fixed and floating structures, and the results of full scale tests are reported.
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Concepts and applications of SEA: Review and extrapolation (A)

P. W. Smith, Jr.

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S97-S97 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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The history of developments in theory, experiments, and applications of SEA is reviewed and compared with that of similar methods of analysis in other fields of acoustics. A summary discussion of basic concepts distinguishes between fundamental hypotheses and hypotheses of convenience. Conjectural extrapolations into the future are offered.
Contributed Papers
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High‐frequency vibration isolation of parallel beams and plates (A)

Robert E. Powell

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S98-S98 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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A statistical energy model has been derived for the flexural vibrational power transmission from a shaft to a point‐connected flat plate. Coupling loss factors from shaft to plate are calculated using infinite beam and plate impedances along with lumped‐parameter impedance models of the shaft support. The support is initially treated as a simple mass, transmitting point forces only. Experimental measurements of coupling loss factor for this configuration show very good agreement with the predicted values. The model is then exercized by introducing a spring, first between shaft and mass, then between mass and plate, and finally between two halves of the mass. The implications of the results for vibration isolation problems are discussed. [Research supported by NSF.]
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A simplified model for the prediction of airplane interior noise by the statistical energy analysis (SEA) method (A)

Balakrishna Dattatraya Thanedar

J. Acoust. Soc. Am. Volume 65, Issue S1, pp. S98-S98 (1979); (1 page)

Online Publication Date: 11 Aug 2005

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Prediction of interior noise essentially represents a definition of attenuation of noise through a sidewall structure. It is a combination of response of the fuselage primary structure to the excitation and subsequent vibration and reradiation. In the cabin noise study, the cabin interior space is an indirectly excited subsystem, the surrounding exterior space is the directly excited subsystem and the fuselage shell structure forms the barrier. The important paths of vibrational energy exchange are mechanical and acoustical. The mechanical connections between the fuselage skin, stringer, frame, vibration isolator, and trim panels provide for the transmission of energy from the exterior space to the interior space by a mechanical path. The flow of vibrational energy via the sidewall cavity is by an acoustical path. The frames and stringers as well as the skin are the elastic structural elements that are capable of being excited under resonant, coincidence and nonresonant conditions. For a typical fuselage structure the frame coincidence frequency is about 80 Hz and the stringer coincidence is about 300 Hz. A typical skin coincidence frequency is 12 000 Hz. This indicates that in an ultimately desired basic SEA model, an appropriate representation for the primary fuselage structure, particularly for adequate low to mid frequency region, is to preserve the identity of all the three basic elements skin, frame and stringer. This makes the model very complex (Fig. S‐1). Initially as a first step to SEA capability an alternate simplified model of intermediate complexity is considered. In this simplified model (Fig. S‐2) the frame and stringer stiffened shell is replaced by an orthotropic shell of an equivalent stiffness. In addition it is assumed that mechanical path is secondary in importance to the acoustic path and can be eliminated as a first approximation. The method for the energy flow calculations and the evaluation of the parameters for this model has been programmed on the CDC6600 computer. The SEA cabin noise computer program has been used to calculate 737 fuselage skin vibration and interior noise levels. Figure S‐3 shows calculated and measured 737 skin vibration levels for takeoff. The predicted values of the present analysis, with orthotropic representation for the fuselage shell are seen to compare quite well with the measured ones. Figure S‐4 compares calculated and measured 737 interior noise levels for a ground engine run. In the low‐ to midfrequency range the SEA predicted interior noise levels is about 2 dB higher than the noise levels measured on a 737 during a ground engine run test (Fig. S‐4). The limitations of the simplified model are discussed and the further planned analytical modifications are outlined.
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